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A desk phone that restarts on its own, sometimes mid-call, almost always has a power or cabling problem at its network port. Work through the checks below before assuming the phone is faulty.

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Note the scope first

Knowing how many phones are affected makes the fix easier to find:
  • Is it one phone, a few phones, or every phone?
  • Are the affected phones in the same room or plugged into the same network switch?
A few phones in the same area point to a power or switch problem. Every phone at once points to a network or service issue — see Troubleshooting.

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Checks you can run

1

Swap the Ethernet cable

A cable with an intermittent break causes reboots without any visible damage. Try a known-good cable.
2

Move to a different port

Plug the phone into another port on the switch, or a different switch. If the reboots stop, the original port was the problem.
3

Check the power source

If the phone draws power over the network cable (PoE), move it to a different PoE port. If it uses a separate power adapter, swap the adapter.
4

Watch the switch load

If several phones on one switch reboot together, especially during busy periods, the switch may be drawing more power than it can supply. Spread the phones across more ports or a second switch.
If reboots continue, watch the phones for a day or two and note which extensions reboot and at what times. That pattern helps support narrow down the cause.
Contact support if a phone keeps rebooting after you’ve tried a new cable, a different port, and a different power source, especially if the reboots happen during calls.