what is the use of this permission in this app

Based on a search of your project’s code, the permission READ_CALL_LOG is not currently used and is not present in your AndroidManifest.xml.
However, you do have READ_PHONE_STATE in your manifest:
Manifest

Merge Into Manifest
Purpose of these permissions in an Alarm App:
Typically, alarm apps use READ_PHONE_STATE (and sometimes mistakenly READ_CALL_LOG) for the following reasons:
1. Silence Alarm During a Call: To detect if you are currently on a phone call when the alarm goes off. If you are, the app can choose to play a quieter tone, vibrate only, or wait until the call ends so it doesn’t blast the alarm in your ear while you’re talking.
2. Auto-Dismiss/Snooze on Incoming Call: To automatically snooze or stop the alarm if a call starts ringing at the same time.
Recommendation:
• If you don’t have code handling phone states: You should remove READ_PHONE_STATE from your manifest. Google Play has very strict policies regarding “Sensitive Permissions” (like Phone and Call Logs). If your app doesn’t absolutely need it to function, they may reject your app or require a complex declaration form.
• Regarding READ_CALL_LOG: Do not add this permission unless you are building a dialer or a call-blocking app. For an alarm app, READ_PHONE_STATE is sufficient to check if a call is active.