I take the pants that have insufficient pockets to a tailor, and ask them to extend the depth of the phone pocket. You can even ask them to do the extension in phone size if you want to restrict its movement in your pocket. On average I've needed about a 3" extension which both restricts lateral phone movement, and also carries it low enough on my thigh that the phone doesn't pinch into my hip when I sit down.
$30 or so later you'll have an integrated Pholster and don't have to carry another thing around with you. For $200 you should be able to update all the pants you have that lack a proper pocket. This is also an incredibly easy thing to sew yourself, by hand, while you watch TV. $30 for a tailor to do the first pair to give you a template to follow, $50 at a craft store will get you some decent scissors, needle, thread, and a yard of whatever material you like. You'll butcher the first pair of pants, but the second, will be better and the third will be perfect.
$30 or so later you'll have an integrated Pholster and don't have to carry another thing around with you. For $200 you should be able to update all the pants you have that lack a proper pocket. This is also an incredibly easy thing to sew yourself, by hand, while you watch TV. $30 for a tailor to do the first pair to give you a template to follow, $50 at a craft store will get you some decent scissors, needle, thread, and a yard of whatever material you like. You'll butcher the first pair of pants, but the second, will be better and the third will be perfect.