NEVER use compressed air to clean a phone. It will NOT clear out the dust, it will force it further inside.
I don't disagree with you in part...yes, the dust may blow inward rather than outward, but any airflow in at one spot will result in an equal amount of air flowing out in others. The rule of "path of least resistance" applies here as it does in any "leak", whether gas or fluid. So the compressed air will cause an airflow, and the result will be SOME air flowing out and with it, HOPEFULLY the dust around the lens of the camera.
The preferred method in my opinion would be suction rather than pressure. The problem with pressure (or compressed air) is it comes with other things...mainly moisture. When ambient air is compressed, the humidity in the ambient air is also compressed, so the result is a higher water to air ratio, or better said a higher moisture content in the air that is blowing out of the nozzle. There is also the possibility that along with that higher moisture content is lubricant from the compressor cylinder (which is usually lubricated with light oil).
If you use not compressed "air", but instead compressed GAS as in the over-the-counter cans, you avoid the moisture, and also the "lubricants" and are likely to have an inert gas (not to mention the lack of fragments or airborne particles), that will do NO harm to the phone.
However there is ONE perhaps notable advantage to compressed air over suction...the lack of microscopic fragments that were filtered out by the intake filter on the compressor. Whether the benefit of the lack of fragments is outweighed by the potentially contaminating oil and higher moisture content (remember, this is an electronic device with highly sensitive componentry and traces on the board that are only fractions of milimeters apart, and moisture or water conducts electricity), is debatable. If suction is used, you avoid the increased moisture from the compression and you also avoid the potential oil contamination as well, but you don't avoid sucking into the phone airborne contaminants (mainly...you guessed it, DUST).
This entire process would be best done with suction and in a "clean room" or "clean containment" instead.
My second choice would be compressed gas in a can off the shelf.
My third choice would be suction in an open air environment, and OUTSIDE (which is actually more free of airborne particles for the most part than indoor air - especially after a rain storm when the PPM is extremely low).
My LAST choice would be compressed air from a home or shop air compressor.