People do not make functional DIY cell phones all the time.

I don’t care if you can hack together something in your garage, it’s not a phone unless it can make calls using cellular infrastructure. That requires licensing, contracts, and business connections to the providers.

A project like that is good for making shortwave radios to avoid Israel installing bombs on your battery, but not useful for this specific purpose outside of making a prototype model to maybe be able to beg for money from investors.