I have a Canon550D, and I would like to shoot a movie using an external microphone.
Can I use a phantom alimentation-required microphone on it?
Not directly, no. You would need to use a mobile preamp/mixer unit (all of the current units I've found are at least dual-channel mixers as well as preamps) that can supply phantom power to the microphone and "lifted ground" audio to the camera (that is, audio without the phantom power voltage offset, which could harm the camera's electronics).
One such unit is this one (link is to a product page at B&H Photo and Video -- I have never used, nor am I endorsing, the product). It certainly isn't the only such unit on the market, but I'll leave it to you to shop around.
If you are shooting from a tripod or dolly (or are using a Steadicam) and can incorporate a small laptop into the mix, there are a whole bunch of USB and Firewire units available as well from the usual suspects in the digital audio workstation world (AVID/M-Audio, AKG, and so on). Latency might be a problem, though, if there's digital doings in the chain, so you'd need to test.