getID3 doesn't decode any audio so no it's not possible with getID3.
Something like mp3gain
will analyze both actual peak volume and subjective overall volume which is perhaps more complexity than you need. Anything that will decode the MP3 audio stream to PCM will let you find the peak sample relatively easily. I don't know offhand of any simple PHP solution (but that doesn't mean one doesn't exist, I just don't know of any).