Cordless phones which operate on the 2.4GHz frequency often cause interference for 802.11b wireless devices. A common step to help stop the interference, or at least alleviate the severity of it, is to change the channel on which your access point broadcasts. If you know how to login to your router's web interface, then please do so. In the wireless section, there should be a setting referring to "channel"; by default this is usually set at Channel 6. Try change it to channel 11 and see if the issue still occurs; if it does, try channel 1.
If you don't know how to login to your router's web interface, please list the make and model of your router -- of course, I'm just making an assumption that you actually have a router in your network setup; if not, please provide a little more detail on how you have everything setup (i.e. hardware).
If this doesn't resolve your issue, you could try moving either the phone, or your access point so that they aren't so close together.
Edited by Dan, 11 February 2009 - 05:06 PM.