power leaking from device via USB
The main properties you want to work around are the maximum allowed reverse voltage, the forward voltage drop, the maximum forward current and the form factor.

The maximum reverse voltage should be comfortably greater than the USB voltage (5V) - give it at least 6V. Practically, you'll probably find a much higher reverse voltage limit in the diode you select, so don't worry about this too much.

The forward voltage drop should be very low at the current you expect to see when the phone is charging. Depending on your phone it should certainly have a charge rate of less than 2A. You'll have to examine the V-I curve for the diode to determine this. Lower is definitely better here - try for .5V or less at 1A or lower.

The maximum forward current is chosen based on the charging voltage of your phone - again, 2A is generally the maximum charging current you'll see from any USB device (and it's generally pads that draw this, not phones) and you'll want a margin of error, so go 3A or above.

For the form factor you'll probably want a through-hole diode for ease of install. I recommend some heat-shrink around the whole thing to give it some mechanical stability when you're done soldering.