Is my daily phone use still straining my eyes even though I don’t experience any symptoms related to eye strain?

No, but I bet you look stupid staring at a little plastic rectangle all day.

Yes, it's possible that something like that could be happening. I was in front of a phone and computer all day for years... I was fine for a while and nothing in my life changed, but bam - I got chronic dry eye all of the sudden. My eyes are scary and red all the time now. It helps when I don't use screens.