There could be some reasons why your calls are not being logged automatically on an Android phone. However, before reporting, please bear in mind that calls can be logged with a delay if you make lots of back-to-back calls during the day. Therefore, if you're sure that these points below are not your problems, please give Salestrail some time.
1. Make sure your Salesforce connection is set with Production instance and you have set your call logging mode to automatic.
2. Check your Office Hours settings (calls taking place outside of office hours are discarded).
Tip: if you want Salestrail to work 24/7, deselect every day.
3. Check if the calls you're looking for are in Unlogged Activities.
If your previous calls show up in the Unlogged Activities tab on automatic call logging mode, there are 3 possible reasons:
The numbers you call are not correct, comparing to Salesforce. For instance, on Salesforce, contact X has phone numbers of 012345678. However, you called 087654321 instead.
No matches: this happens when Salestrail cannot match the phone number to a contact / lead on Salesforce. In this case, you can add a new contact / lead to log the phone call to. See instructions here.
Multiple matches: this happens when a phone number belongs to more than one contact / lead. You can either clean up the duplication on Salesforce, then come back to Salestrail to log the call OR tap on the call and choose which contact/lead you want to log the call.
4. Phone settings
Make sure you've set up your handset as recommended by us!
Check that your battery optimization is off for Salestrail: the most usual path is going to Apps > Salestrail > Battery optimization.