Because phone manufacturers don’t open source their firmware, you probably won’t be able to get Linux on an off-the-shelf phone. (Please someone correct me if I’m wrong).
Your best bet, if you want to go down thus route, is to get the PinePhone Pro. It’s relatively affordable.
Before you try anything, think hard about your relationship with your phone and what you expect from it. Does work require you have an app installed? What kind of apps do you use regularly? You won’t have things like: CVS for meds, AA for flying, Steam for 2fa, Signal, Telegram, google maps, etc. Some you might be able to use their webapps, but the browser might be a bit sluggish because it’s the full desktop version. Firefox isnt fully mobile friendly. Battery life won’t be what you’re used to. Linux on the phone is just like your regular Linux, so you’ll have the stuff your used to from there, and you’ll having calling, sms, mms, and voicemail.
I have the PinePhone and the Librem 5, but I still use my android.