I think Phil really emphasized this when he was talking about shopping shortly after (or possibly even shortly before?) lockdown really became a thing. He acted like it was a big deal he was able to buy items without people being in a panic and fighting over items. Along the same lines, when he talks about why he doesn't shop at Walmart for basically the same reasons, thinking it's a public brawl or something. You only get that level of paranoid when you're constantly shut in your house, refusing to step outside the few safe spaces you've gotten used to, which for Phil, sounds like the mall and Kat's place of work, assuming that's where he does his grocery shopping.
I think that's a large part of why he's struggling with any of his medical appointments. Well, the vaccine at least, I think the ear infection nonsense is just a lie, and that's why an appointment never materialized. But with the vaccine, you can tell how scared he is to go without his mom taking him.