• Conjure Animals: level 3 / 1 action / 1 hour / CR 2
• Conjure Woodland Beings: level 4 / 1 action / 1 hour / CR 2
• Conjure Celestial: level 7 / 1 minute / 1 hour / CR 4 (+1/2)
• Conjure Fey: level 6 / 1 minute / 1 hour / CR 6 (+1)
• Conjure Elemental: level 5 / 1 minute / 1 hour / CR 5 (+1)
• Conjure Minor Elemental: level 4 / 1 minute / 1 hour / CR 2
• Summon Greater Demon: level 4 / 1 action / 1 hour / CR 5 (+1)
• Summon Lesser Demons: level 3 / 1 action / 1 hour / CR 1
• Infernal Calling: level 5 / 1 minute / 1 hour / CR 6 (+1)
• Giant Insect: level 4 / 1 action / 10 min / CR 3

Above are all the currently-existing summoning spells, with level, cast-time, duration, and CR limit - with upcasting specified in parentheses.

From this we can see a couple trends. Fiend summoning does play a bit of an exception, so we'll address that last.

1. 1 hour duration for nearly everything
2. 1 minute cast time for anything above CR 3, and the only spell that gets you CR 3 at 1 action is specifically a Giant Scorpion, not a choice of CR 3 creatures*
3. CR is capped at the level of the spell for high levels (5+), and strictly lower for low levels (4,3)*
4. Minimum level is 3
5. Upcasting increases CR only for high level spells (5+)*

*Fiend summoning carries personal risk, and as such is allowed to break some of these rules - notably with Summon Greater Demon only costing an action for a CR 5 creature, and both Summon Greater Demon and Infernal Calling getting a CR higher than the spell level.

Now let's consider Magnificent Summoning in context.

• Magnificent Summoning: level 1 / 1 action / 1 minute / CR 1 (+1)

It is lower level than any existing summoning spell. This is of course your intention, so let's table that for a moment.
It costs only an action. This isn't out of the ordinary, but tends to restrict the power of the summoned creatures considerably.
It only lasts 1 minute. This is a big downside, but it's also a big downside that doesn't really mesh with all the other summoning spells.
It summons a CR 1 creature, and matches the slot level with CR for upcasting. This is powerful. It's traits that we only see in level 5+ spells, plus the 4th level spell that puts you and the party in danger.

All together, this spell is strong. Especially being able to summon CR 1 creatures as a level 1 character - which is significantly better than adding an extra PC to the party at that level.
It matches (through upcasting) the strength of the higher-leveled summoning spells - why bother with any of those if you have this?
It strictly outperforms the lower-leveled summoning spells when equivalently upcasted.
In fact, its only downside is that it only ever lasts for one combat - a downside that is DM-dependant to ever even matter.

This is not a spell I would allow any player of mine to use - it would trivialize low-level encounters, it matches or exceeds the effectiveness of all higher-leveled summoning spells, and it appears to be overpowered-with-a-big-weakness.

It's overpowered

As SeriousBri points out in his answer, this ability is pretty much busted for any kind of spell level, but as you've currently worded the spell, it's especially problematic for Wizards and high AC classes like Eldritch Knights and Paladins.

If you're already rocking 20+ AC, most things that will hit you are either crits, or a spell of some sort, which means you're looking at only getting damaged once per turn. This makes the spell rather insane for Eldritch Knights and Paladins, who can simply pop this spell and keep concentration on it until it blocks a crit or a spell, and then recast it if the fight isn't over yet. The fact that it is a bonus action makes this especially troublesome, because it's often not that hard to find time to cast a bonus action, the spell would be a lot less 'must have' if it required a regular action, it prevents stacking Dodge ontop of this spell, making you almost impossible to damage for a turn.

For Wizards, this spell will break the game somewhat at level 18. Most games will never get to that point, but a level 18 wizard can pick a first level spell and basically treat it as a cantrip, casting it whenever you like as long as you have it prepared. I can't think of a single first level spell that I'd take over the ability to block a damage source per turn for a bonus action.

That's not even taking upcasting into account. I've played an Eldritch Knight focused on tanking, and this spell would have basically replaced all the other spells I used.

You're essentially trying to make a less powerful version of Resilient Sphere, so perhaps looking into the restrictions that spell puts on you will make it more manageable. Also changing bonus action to normal action will greatly depower the spell, turning it into a less good-for-every-situation spell.