The latest and most official rule for 3.5 is from Libris Mortis, which states that a lich cannot create a second phylactery at all, even if the first is destroyed. This contradicts (and supersedes) an earlier (3.0) rule from the Savage Species Lich Template Class. Many thanks to @ColinD for linking those.
Note that if you do not have Libris Mortis or that particular Savage Species web enhancement in play, there is no rule on the subject at all. The lich monster entry states that the purpose of the phylactery is to store the lich’s life force in it, and then goes on to describe how it is made: with no restriction mentioned, it seems possible to create more than one, but the role of the phylactery during the ritual itself and the uniqueness of one’s own lifeforce may imply that the process cannot be repeated.
Note that resurrection and true resurrection return an undead creature to the life they once had. If nothing else, even in the case of Libris Mortis, a lich could do that and then repeat the process of becoming a lich, creating a new phylactery. Any living creature is eligible to become a lich; there is no requirement that they cannot have been a lich previously.
If Libris Mortis is not in play, this can even done to the remains of a destroyed lich, but with Libris Mortis, there is a clause that “If a lich without a phylactery is slain, the lich is forever destroyed.” Whether that only means in the automatic fashion typical for liches, or at all under any circumstances (and whether that is going to trump the rule that undead can be restored to life) are all very ambiguous questions that need to be answered by the DM.
Finally, the dry lich (Sandstorm) may have different rules, since they start with several phylacteries.
A warlock following a patron of The Undying
In the new Sword Coast Adventurers Guide (page 139), The Undying patron is detailed. This seems to suit your needs exactly, although you might not be able to change from one class to another without your DM's permission.
Listed as example Undying are actual liches like the lich-queen Vol, Vlaakith the lich-queen of the githyanki, and "sentient wizard zombie" the deathless wizard Fistandantalus, among others.
Your alignment is not tied to your patron, and you can read about that here.
The Undying expanded spell list includes spells like contagion, death ward, false life, ray of sickness, speak with dead, and other lichy type things. The following features are paraphrased, so you'll need to grab a Sword Coast Adventurers guide to get specifics.
Among the Dead
At 1st level, you learn spare the dying and have advantage on saving throws against disease. Also, when an undead creature targets you, they make a Wisdom throw against your spell DC and can't target you on a failed save. They are immune to this for 24 hours if they succeed or if you target it with an attack or spell.
Defy Death
At 6th level, you gain 1d8 + Con hit points when you succeed on a death saving throw or use spare the dying once per long rest.
Undying Nature
At 10th level, you can hold your breath forever and don't need food, water, or sleep. You also age 10 times slower and can't be magically aged.
Indestructible Life
At 14th level, you can use a bonus action to regain 1d8 + warlock level hit points. You can also reattach severed body parts when you use this feature. can use once per short or long rest.
So, while not technically immortal, this is pretty close for RAW and requires no homebrew unless you change from your current class to a new one. An elf Undying Warlock can live to be about 7000 years old, which is really enough time for you to roleplay until you actually die of old age in real life.
Best Answer
This plan won't work (unless your DM allows it)
You are unable to create a phylactery purely out of salt
According to the Monster Manual entry for lich:
Assuming you got a chunk of salt large enough that you can hollow it out it still has to have runes scribed in silver which means the phylactery can't be purely salt. And silver is not going to dissolve in water like salt would. Thus, the plan of dissolving the entire phylactery is not going to work as expected.
Dissolving a phylactery would destroy it
If you dissolve your phylactery you destroy it. Dissolving is the act of destroying the chemical bonds of something and allowing the physical form to be completely broken down. However, in the case of a phylactery that physical form is required. There has to be a tangible object that souls can be fed to. And that object must have a cavity and have silver runes scribed on it. When the phylactery dissolves it meets none of these requirements. And neither does the ocean at large.
Dissolving a phylactery would be very difficult if not impossible
It is unlikely that simply submerging a phylactery in water would be enough to destroy it. Phylacteries are powerful magic items and would likely not be able to be destroyed by the simple act of submersion in mundane water because of the powerful magic energies that power it and hold it together.
So what happens if you submerge a salt phylactery in water? Either it will be destroyed by dissolving or it will simply be unaffected by the water. Neither option allows you to make the whole ocean to be your phylactery.
There are no rules for PC liches
Even beyond what I talked about above it is worth mentioning that this entire scenario is already outside the scope of the rules essentially. There are only rules for DM controlled liches and no options exist for PCs at all. So the DM is going to have to create the rules for it on the fly with little to no guidance from the rules.