Ok, but there is a lot of power to be saved. If you can prevent the beam from going in the "opposite" general direction, you can already save 50%. I'm not convinced there is nothing to be gained by using a small array.
And even then, you will need individually controlled phase shifters for each array element, adding cost, complexity and mostly negating energy savings.
Edit: All of that in addition to the problem that you need to know the location of the base station and have you array antenna roughly oriented towards it.
Then however much the phone is tumbling, you'll always be exactly sending the data in the right direction.
Turns out the problem is moot anyway - unless you have a huge antenna to get a really narrow beam, sub-degree positional errors won't make any impact.