Phantoms do not have a mob cap, causing performance issues

I wouldn't call this a "bug" if you're playing in a modded world in perma-night

I think the OP meant to say 'mob', not 'mod'.

Right, this is not modded, these are vanilla features.

@unknown Is not modded if you use ingame commands, even mojang has do it easier to change lot off stuff before you even load the world.

At not have mobcap on phantoms are likely stupid when they not have mobcap on fish (the way they limit fish was squid). So if you remove squid, you end up with 1000 of fish (it should be fixed now).

Or is this counted as modding too?

If repairing elytras is your main concern, one workaround might be to enchant the elytras with Mending and then disable phantom spawning. Then, you could repair your elytras with an experience farm without having to hunt phantoms. This workaround has the additional advantage that repairing the elytras won't incur a prior work penalty.

Getting mending books might be difficult, though, since villagers don't restock their trades at night. You would probably have to fish for books. (You could use villagers, but you would have to keep getting new ones when the old villagers run out of stock.)

We decided as a group not to disable phantoms since the beginning.

A bunch of the members do not want to disable the phantoms, they don't want us to just continue changing game rules whenever we have an issue. 

It's like saying, "There are too many mobs so we will just use the /gamerule disablemobspawns command". This is not the correct way around the problem.

We make decisions as a group, so now that the rules are set... we just kinda got to live with it until Mojang does something about it.

Btw, I am not spending half my day to get a few mending books. I have no idea how to make an experience farm.

Having a way to reduce the impact of a bug from a gameplay prospective, by disabling a feature of the game, is NOT a workaround.

This is pretty bad, i had 50 of them and died in a hardcore world.

I recently had the same issue. We decided to made a datapack which makes time in minecraft like real life. We made it run on est time. Although, we play till midnight. It's basically impossible to play at night. There's prob around 80 phantoms in unloaded chunks near my base. It's actually insane, when did Mojang start adding randomly spawning creatures with no limit and restrictions. The wandering trader, phantoms, and patrols. It's actual garbage.

The worst part is that we have the same issue at OP, we don't want to have to disable them completely, we just want them to be balanced in the game. I usually only play starting at 8:00 when the sun is already down, there are some chunks I can't go near since I know that I will be attacked by hundreds of phantoms.