That building is now the headquarters for the Phoenix Dream Center, a non-profit organization "committed to stopping human trafficking, educating tomorrow's leaders, and ending childhood hunger". In short, it appears to have been converted into a homeless shelter.
The "Tours" page on their website shows an aerial view that is clearly the same location - right down to the position of the palm trees!
Based on a Google Search of the address prior to that it appears to have been the "Comfort Suites Conference Center Hotel" and possibly prior to that the "Villager Premier Suites & Conference Center", although it's not clear if either of those were it's name in 1999 when you were there.
The "GR" and other signage is indeed "Gregory's Grand Adventure" which appears to be one of several "Gregory's" restaurants located from California to Texas. This Tweet includes a matchbook showing their addresses, and confirming the address of the above property as 3210 Grand Ave, Phoenix. It also shows that the hotel was an Embassy Suites Hotel at the time - which is potentially what it was at the time you were there.