What is the value of the company's facility in Phoenix as a percentage of the total square feet of all its facilities in the U.S.?
{"Boston": {"State": "MA", "Country": "USA", "Sq ft": 31752, "Type": "Lease", "Business Nature/Use": "Administrative, sales, client support, R&D, engineering, professional services"}, "Panama City": {"State": "FL", "Country": "USA", "Sq ft": 51288, "Type": "Lease", "Business Nature/Use": "Administrative, sales, client support, R&D, engineering, professional services"}, "Belfast": {"State": "NI", "Country": "UK", "Sq ft": 15500, "Type": "Lease", "Business Nature/Use": "R&D, engineering, administrative"}, "Phoenix": {"State": "AZ", "Country": "USA", "Sq ft": 4865, "Type": "Lease", "Business Nature/Use": "Data Centre"}, "Philadelphia": {"State": "PA", "Country": "USA", "Sq ft": 14183, "Type": "Lease", "Business Nature/Use": "Administrative, sales, client support, R&D, engineering, professional services"}, "": {"State": "", "Country": "", "Sq ft": 117588, "Type": "", "Business Nature/Use": ""}}
phoenix_sq_ft = df["Phoenix"]["Sq ft"]
total_sq_ft = df[""]["Sq ft"]
answer = phoenix_sq_ft / total_sq_ft * 100.0