Quick question...
Is the basic spot for illegal touching the previous spot?
First you must classify the play. This is a legal pass play, so this is a loose ball play.
The basic spot for a loose ball play is the previous spot.
If the offense fouls down field, the penalty is enforced from the previous spot.
If the offense fouls in the offensive backfield, the penalty is enforced from the spot of the foul. This is the "but one" in All but one.
Just remember for penalty enforcement, you must always go through all 4 steps.
1) Classify the play.
2) Determine the basic spot.
3) Who fouled and where?
4) Enforce using All but one.