IN the envirornment you describe, power  is probably limited to 100mw,
although you should be able to ask T-mobile about it.  Also the gain
on the antenna says they are not omni directional, so if  it is 5 feet
away, I assume it is about 5 feet above you. The pattern from the
antenna probably puts out almost no energy either straight up or
straight down. It doesn't do any good.

There are no proven hazards to exposure at that sort of level, and
while many claims have been made, none of the claimed results has been
reliably reproduced under controlled conditions.

By the same  token military and police have been exposed to higher
levels for much longer periods of time, and we don't seem the dropping
like flys from various forms of cancer.

In short there may be a hazard, but it cannot be much of a hazard
because it hasn't been quantitified yet, i.e. it is within the noise,
so does not materially the risk above normal background.