What happens when the phone only rings once?
Thereof, how many times does the phone ring when you are blocked?
If you hear only one ring or no ring at all before your call goes to voicemail, this is a good indication you're blocked. In this case, the person has used the number blocking feature on their phone. If you call once a day for a few days and get the same result each time, that is strong evidence your number is blocked.
Correspondingly, will the phone ring if you are blocked?
If you call a phone and hear the normal number of rings before getting sent to voicemail, then it's a normal call. If you're blocked, you would only hear a single ring before being diverted to voicemail. If the one-ring and straight-to-voicemail pattern persists, then it may be a case of a blocked number.
One ring. Repeated redirects to voicemail after a single ring, or none at all, could be an indication your number is blocked. If you hear multiple rings before hearing the voicemail prompt, chances are the person has not blocked your calls but is just rejecting them.