Air carrier Captain reported Taxi Spot 1A at PHX is not depicted on any publication. The Captain stated ground control issued taxi instructions containing reference to Spot 1A.

Narrative

We landed at PHX on Runway 8. Tower cleared us to turn right onto Taxiway B9; join S; and contact south Ground Control. The FO called South Ground on the Sierra bridge and told them we were headed to Gate Y. We thought we heard ground say Taxi to the gate via 1A". We discussed and neither of us had any knowledge of a Spot 1A. We checked the AMM (Airport Moving Map) chart and saw no depiction of a Spot 1A. Given this and the definitive company information guidance to NOT cut across directly from S to Gates X; Y; Z; and A we thought we misheard him and continued to Taxiway D and made the two left turns to go over Spot 1 to Gate Y. After we passed Spot 1 northbound towards the gate; we noticed a newly-marked (new to us anyway) Spot "1A" to the left located almost directly behind Gate Y with a taxi lane; leading off of S to Spot 1A; providing a much more direct access from S to Gates X and Y. Ground Control did not say anything about our altered taxi routing via D. After block-in; I re-checked every chart to include the AMM; airport information; and even the satellite view. No chart or document I could find had any depiction or mention of spot 1A whatsoever.Suggestion: If PHX Ground is going to continue to use this spot; it needs to be charted ASAP."