This app was mentioned in 10 comments, with an average of 2.70 upvotes
Sure, I'm on Android and use this: https://play.google.com/store/apps/details?id=com.cameronzemek.nSuns531LP
It's not as nice as the stronglifts app as it's made by a third party (a redditor whose name I don't remember), and I think the "history" section could be improved a little, but it gets the job done anyway.
There actually is an app - a few I'm pretty sure. The one I tried using can be found on Android here. Not sure if an iOS variant exists.
Personally I'm old school and resort to a bringing duotang with printed spreadsheets where I can make comments in the margins like if I'm feeling great/horrible on that particular day etc.
nsuns 531 is a good mix of strength and volume.
edit: here's a great app on google play.
What??????
Here's a link
https://play.google.com/store/apps/details?id=com.cameronzemek.nSuns531LP&hl=en
Here's the link https://play.google.com/store/apps/details?id=com.cameronzemek.nSuns531LP
Found it here in this sub as well :)
There's an actual nsuns 5/3/1 app on the Android store that's been quite useful. Don't know if it's on iphone tho.
https://play.google.com/store/apps/details?id=com.cameronzemek.nSuns531LP