Issue with phone not ringing. Coming up as currently busy

Using Asterisk on the FreePBX distro

The phone is not set for DND. However, some calls go through and the phone rings normally. Other times it doesn’t ring at all with the the user getting a busy message voicemail.

“sip show peers” comes up around 70-100ms.

Even when the phones gives busy message status is always OK and registered.

Is there any way to troubleshoot this phone and see what’s going on?