I would like to know if I need a transit visa if I transfer from Heathrow terminal 5 to three. I will only be staying there two hours as I will be flying to Geneva. I am a Philippine passport holder.
If your transit time is less than 24 hours and you are from the Philipines, you will not need a transit visa as long as you will stay in the arrival/departure lounge. This is called airside transit. If you need to go out from this lounge or need to stay more than 24 hours then you will need a visa.
In your case (from the Philippine, 2 hours connection time), UK border agency website says:
Yes, you generally need a visa to transit the UK (unless you will arrive in the UK by air, and leave the UK by air less than 24 hours later)
In addition to that, Heathrow airport has a nice service for transit passengers. Heathrow airport website describes how to transfer from terminal 5 to 3 without the need to pass through passport control.