Asked what issues the guests would think Grange Hill would explore if on air today, Lord Grade suggested mental health and family relationships.
"These are big stories today, and very emotionally engaging," he said.
Choosing rising prevalence of misogyny, Ms Gayle said: "I think there's a real conversation to be had around TV getting a grip, getting young boys to watch so they are outside this toxic echo chamber [of social media]."
Sir Phil said social media itself would be the issue to tackle.
"There's no counterpoint to that, and that's what Grange Hill used to offer," he said.
"It didn't matter what the issue was... Grange Hill would always offer some solution or some way to go and ask somebody about this issue, but at the end of it, it's basically, you're not on your own."