It could be a phone fault, but if it's working OK I'm inclined to think not. And if the phone hasn't changed, then it's fair to assume the TV signal has got weaker, and hence more easily swamped by the same phone radiation.
Has your region yet gone fully digital? Prior to the digital switchover, most of the digital transmitters were/are being run at reduced power, to avoid interfering with analogue. It's possible that they may have had to re-adjust the signal strength, hence reducing power even more, that seems to have happened in our area such that the ITV channel group is rarely watchable these days.
It's also possible your TV aerial or downlead has got damp, or deteriorated in some other way, over the winter. After the full digital swicth-over the transmitter powers will generally be significantly increased, so problems like this may simply evaporate.
