Microsoft BASIC for 6502 – Original Source Code (1978)
looks like there is a PHP intruction.    TABER: PHP			;REMEMBER IF SPC OR TAB FUNCTION.
	   JSR	GTBYTC		;GET VALUE INTO ACCX.
	   CMPI	41
	   BNE	SNERR4

also it appears right in the middle    FRETMP: STWD	INDEX		;GET LENGTH FOR LATER.
	    JSR		FRETMS		;FREE UP THE TEMPORARY DESC.
	    PHP				;SAVE CODES.
	    LDYI	0		;PREP TO GET STUFF.
	    LDADY	INDEX		;GET COUNT AND

http://www.obelisk.demon.co.uk/6502/reference.html#PHP