How do I AirDrop from a MacBook to its tethered iPhone? My MacBook (OSX Yosemite 10.10.5) is tethered to my iPhone (10.0.2) in order to provide Internet access.

How do I AirDrop from my Macbook to an app on my iPhone?

Currently I have to use Dropbox, ie. move the file into Dropbox, wait for the (possibly large file) to upload, then download it on my iPhone to the desired app (causing another sync).
You will need to turn off Personal Hotspot before you can AirDrop.

AirDrop transfers data over Wi-Fi between the two peer devices (in this case, your MacBook and your iPhone). Since your iPhone is providing a Personal Hotspot via Wi-Fi, that connection is not available for AirDrop.

If turning Personal Hotspot off and on repeatedly is too cumbersome, you can provide tethering through USB instead. Then your Wi-Fi connection will always be available for AirDrop.