I dropped my S4 at the gym and did something similar. I cleaned up the glass and got most of it out and then popped one of these on. I ended up buying a S9 in the end but gave the S4 to a relative and still going strong but clearly not waterproof.

https://amzn.eu/d/aFbqA2D

Exercise Physiologist here. It can take 6 months to see meaningful changes but If you are running steady state for 40 minutes I would suggest mixing up 1 of those sessions for a short, higher intensity run.

Maybe only do 20-30 minutes but at a lot higher pace and alternate between the speeds for short durations (200-400m).