By any chance does the wireless router seem to fail more often when the phone is in use?
Many cordless phones use the same 2.4GHz freq as your wireless router, and therefore will create interference when in use. Sometimes changing channels on the wireless router helps (or maybe the phone offers another channel option). Other times you may need to consider a cordless phone that uses another freq (e.g., 5.8GHz) or even a wireless router w/ a different freq (e.g., 5GHz).
Of course the phone might not be a problem at all, but you did mention it.