A destroyed creature with the template class lich refoms up to a few miles from its phylactery
The Wizards of the Coast Savage Progressions Web column "Lich and Weretiger Template Classes" includes in its description of the lich template class's class feature phylactery the following text:
Once the phylactery has been completed, the lich can avoid permanent destruction as long as her phylactery survives. If she dies or is destroyed, she reappears 1d10 days after her old body's death. She gains her new physical form by grafting her undead spirit to a humanoid corpse, mindless undead, or some weak-minded creature within a few miles of her phylactery. The new body has all the abilities and powers of her old one, though any items she used to carry are lost (probably taken by those who slew her old body). Likewise, any spells or effects bound to her old body with permanency do not spontaneously appear on her new one. Most liches who recover from death spend a year or more tracking down their items and learning more about their attackers, and it is not unusual for a lich to wait decades before exacting her revenge.
Emphasis mine. Whether the same is true of all basic liches is unknown, but without additional guidance this seems a good enough rule as any.
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:
A phylactery is traditionally an amulet in the shape of a small box, but it can take the form of any item possessing an interior space into which arcane sigils of naming, binding, immortality, and dark magic are scribed in silver.
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
Destroying a lich’s phylactery is no easy task and often requires a special ritual, item, or weapon.
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.
Best Answer
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.