iPhone turn green then black and is frozen

Two basic troubleshooting steps to perform (test after each attempt):

A) Try a "forced" restart of your device using these instructions: Put it on charge for at least half an hour, then, keeping it plugged in, use these gestures:

In rapid sequence, press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the side (power) button. Only when the Apple logo appears (it might take 10-20 seconds), release that button (ignore all other screens that might appear, the one with the "slider" to turn the device off included).

B) If you can, check your battery status in Settings>Battery>Battery Health & Charging>Maximum capacity. If it is close to 83-80%, have it replaced as soon as possible, since it might have unpredictable behavior.

If the issue still persists, it could be a hardware (battery? digitizer? screen? other internal compoeent?) failure but we, just users like you, cannot diagnose that issue remotely, sorry.

I suggest that you contact Apple Support directly, using this link:--> Contact Apple for support and service , or make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> https://locate.apple.com/choose-country-region . After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.