1. When we create a phone call activity from a record(account, case etc.) > add description > click ok. The phone call activity status: completed.

2. When we create a phone call activity by going to sales > activities > create a new phone call activity and set regard to a record. The phone call activity status: Open.

It is a by design feature, however it would be viable if user could create a phone call activity from a record(account, case etc.) > add description and can keep the activity open if required as it becomes a tedious task for users to go to activities again and again > create a new phone call activity and set regard to a record to keep it open.