Okay got two things...
First is battery holder:
https://www.amazon.com/dp/B08BRNWBMR
It just barely fits around huge top tube. Easy-enough to put phone in and least with my Samsung S22(?) Ultra I can't imagine it coming out ever. It is a little annoying how it covers the 4 corners of phone, so sometimes hitting buttons in corners is hard. Not saying this is best battery holder, but this is at least one that works.
Second thing I'm almost embarassed to say I got.. I wanted a power meter and I want platform pedals and there aren't really many options to pick from, its really just SRM XPower pedals. And they're so overpriced I don't want to support such rediculousness. But I like data. So I got them. Pedal strikes and stupidly expensive pedals seems like a bad combo, so I'm planning to swap as needed and only use them for rides I know pedal strikes won't be an issue.
The actual pedals themselves are just fine. Really its the software that bother me a bit. I've been using Wahoo app on phone for recording rides. After getting Xpower pedals, both pedals have a sensor in them.. so you get left and right data. I add both pedals in Wahoo, go for a ride, post to Strava.. look and power is 1/2 what it should be. I don't know what exactly is not working as it should, but Wahoo says like 220watts and Strava says 110watts.
The pedals have some Zwift-compatibility-mode where instead of adding both pedals as separate devices you only add the right pedal and the left pedal sends it data to the right pedal and it reports all the data. Seems unfortuante but try this mode.. and it was even worse. Both Wahoo and Strava end up reporting ~160 watts.. and I'm confused.. then I see in Wahoo it says left/right balance was like 70% or something. Basically like on leg was producing twice as much power as the other. Which makes no sense. I think what was happening is there was a bad connection and one pedal's data was just missing most of the time... I don't really know how its possible.
I was about to send pedals back I got so annoyed with them. I then try a few other apps, all seem like they have their own issues, and eventually give Cyclemeter a try. And it works. I add both pedals as their own devices, app lets me set one to left and one to right pedal.. and go for ride and submit to Strava and all data makes sense. Cyclemeter app is like $10/year but whatever. I just want things to work.
Riding for last week or two maybe.. fun to track power.