That's a pretty good router if you are getting an excellent signal two floors up. You can try setting the router to use 5Ghz only and see what happens. If it works well right away it should avoid most interference issues. You will at least know if it is able to maintain a link at 5Ghz. If not, then you know that you are subject to 2.4Ghz interference. You would also be able to turn off the 5Ghz band if it doesn't work, no sense clogging up a band that doesn't work for you, and that would stop the possible case where the 2.4Ghz band gets crappy and the bridge tries, but fails, to switch to the 5Ghz band. Then we just have to deal with the phone interference. You can try putting power line filters on both the phone base station and Bridge to make sure you aren't coupling signal that way, and if it's possible to move them farther apart it would help. I suspect the phone is frequency hopping spread spectrum which means it uses the entire 2.4Ghz band so changing channels on the bridge/AP probably won't help, but you could try. Stick to 1, 6, or 11, whichever is least used in your area. Use NetStumbler
to look around at signal levels and channels. If you want to get really techie and impress your friends and acquaintances you could get one of the new generation mini spectrum analyzers like this
for about $35 that will show you precisely what is going on in the interference department, but that doesn't really solve the problem. Let us know what you find.