If the Microphone Button / Mute Button indicator of your SPA9XX Series Phone will blink then turns RED it means that the phone is not detecting connectivity on LAN. Check your physical connectivity to your LAN by looking at the LED indicators on your network and inspecting the cable if it's properly plugged in.
Assembling the Phone and Connecting to the Network
Step 1: Find the end of the coiled phone cord that has the longer straightened end. Plug that end into the back of the phone base (phone symbol).
Step 2: Plug in short straightened end of the handset cord into the jack at the bottom of the handset (not shown).
Step 3: If you are using an external power source, push the power cord into the power supply, and plug the power supply into the phone base unit. Use only the power supply that came with the phone. SPA922 &SPA942 can be configured without external power, if connecting to an IEEE powered ethernet switch. See Linksys.com for details.
Step 4: Plug the ethernet cable into the back of the base station. Plug the other end of the ethernet cable into your already prepared network connection. If the phone is configured using an optional POE (Power of Ethernet) adapter, see that device's instructions to properly set up.