The short answer is that it could interfere with the wi-fi, but your wi-fi should not interfere with your phone because it uses WDECT, "wide-band digitally enhanced cordless telecommunications" engineering. No matter how tight the bandwidth is on any RF transmission, power, proximity, and harmonics all play a roll. Ideally we want the power from our transmission to occupy the target frequency but the reality in RF is that this is nearly impossible without DSP filters. I have pasted some extra info below to help answer this question.
Digital Enhanced Cordless Telecommunications
), known as Digital European Cordless Telephone
until 1995, is an ETSI
standard for digital portable phones
(cordless home telephones), commonly used for domestic or corporate purposes. It is recognised by the ITU
as fulfilling the IMT-2000
requirements and thus qualifies as a 3G
The four most common frequencies today are 900MHz, 2.4GHz, 5.8GHz and DECT 6.0:
Currentlythe most common frequency for cordless phones, 900MHz phones may offera greater range than other frequencies. However, the 900MHz spectrum iscluttered and may result in interference with baby monitors and other900MHz cordless phones. Radio scanners can also easily pick up thisband.
2.4GHzphones offer better clarity and security than 900MHz, but mayexperience some interference with microwave ovens and wirelessnetworking (wi-fi) products.
Themost advanced cordless phones available, 5.8GHz phones transmit on anew, open frequency and have the least chance for interference. Theywill not interfere with wireless networking (wi-fi) products.
DECT6.0 operates on the 1.9GHz frequency. Though newly approved in the US,this frequency has been used for many years in Europe and can increasecall clarity and security. The wi-fi friendly DECT technology easilyintegrates into homes with wi-fi and internet services because the1.9GHz frequency is exclusive to DECT, making it interference free forcordless communications.