It would be very unusual for the RFI to be occurring at the 900 MHz operating frequency of the cordless phone, and much more likely that it's occurring in the "land line" connected base unit.
Try 4-5 wraps of the telephone cord (between the base unit and the wall, very close to the base unit) through a ferrite toroid form of Mix #43, and see if that takes care of the problem. If it does, and your neighbor complains, offer to do the same thing for him.
If the ferrite helps a bit but doesn't quite eliminate the interference, try another ferrite toroid, in addition to the first one! Also, sometimes the interference is conducted into the phone via the power supply which powers the base unit. Most of those are "wall cube" type supplies which plug into the AC mains and then have a long DC cable providing power to the base unit. Wrapping that DC cable through a ferrite toroid close to the telephone base unit often helps eliminate RFI altogether.
In my case (five cordless phones, throughout the house), I had to add ferrite to both the telephone cords and the DC power cords on all the phones to completely eliminate RFI from all bands and power levels.
WB2WIK/6