Can I plug my iPhone 7 directly into the 87W USB C power adapter?

Solution 1:

It will charge. It's not dangerous. That power adapter is designed to supply UP TO 87W. If you plug a 15" tbMBP into it, it will draw all 87W provided. If you plug a 13" tbMBP into it, the MBP will only draw 61W, even though the adapter can provide 87W. Same for you iPhone. It will draw the amount of power it needs (~10W, IIRC), and the adapter has no problem providing only that amount of power.

However, it is interesting to note that the USB plug adapters that come with iPhones provide only 5W, iPhones are capable of pulling more power, and will charge faster when plugged into an iPad (10W) or tbMBP USB plug adapter.

Solution 2:

It will work just fine and won't damage it.

It will charge your iPhone just fine with 2.1 Ampere until it reaches 80 % battery charge. After that point it will charge at a lower rate (also called "trickle charge").

Your iPhone controls how much energy will be drawn, not the charger.

You'd get same behavior if you charge it

• connected to a MacBook Pro Retina (or newer) using a USB port
• using the 2.1A/12W charger from the iPad