SLPT: If you dont feel like wearing pants, you can carry your phone around in that little front underwear pocket* (*male only)

My underwear has an external pocket on each side, no need to slide your phone in the junk pouch.

Do people wear underwear for any other reasons?

Female underwear has a similar pocket, just in the undercarriage

its easier if I just tie my dick around my phone

You don't really have to wear underwear either if you don't want to. Everyone has a built-in pocket between their buttcheeks.