A Stages Dash is like $75 and would be enough for what you're after.
Way way back I avoided the "bike gps" for a long time going with the phone and mounts. Long term, get the bike gps. You won't regret it.
I simply cannot advise on phone apps for this stuff when I don't believe it is the correct way to go. There's some good ones out there, but it is good software on the wrong hardware. I totally get the whole Quadloc case things and all that. But once you've bungled it and damaged a phone you do regret it.
Life is better with the bike gps. Doesn't have to be fancy. Just do it.
After that, just ride a while and get more data. I don't advise open road tests unless you can really be at peace with the traffic and handle that. Going deep can lead to miscues in bike handling. So be careful. Maybe buy a used fluid trainer to use once in a while and be able to do tests and some intervals. Some intervals just aren't great if the routes where you live don't allow for it.