why is my battery pack swelling to cause my screen to pop out?

Hi

Turn iPhone off Make an appointment at Apple store DONOT use iPhone

You could cause a fire use SIMCARD in other phone if you have one.

Cheers

Brian 🇬-1F1E7;

Is this a third-party battery pack? Regardless, it sounds like the battery is defective and I would stop using it immediately until you can get it replaced.

iPhone Repair - Battery & Power- Apple Support