Greetham-Clark had uploaded a video of Norma talking about her wish to meet the former Take That musician to social media, which was viewed over a million times.
Williams was tagged over 5,000 times by fans before his team arranged the 25-minute call.
“The news and the media that came with it made Norma feel so special,” Greetham-Clark added.
“She felt like a superstar.”
Williams said on the call that he hoped to meet Norma in person next time he was in the UK.
On Friday, the singer reached number one in the album chart, with Britpop – his 16th album as a solo artist. Williams now has the most number one albums in UK chart history, surpassing The Beatles.