For what it's worth, our secondary banned all phones (and smartwatches etc) outright this year. They don't specifically state phones are banned on the commute, but effectively they are, because they are not allowed on the school premises and there is nowhere to hand them in. (I'm completely against this. I think brick phones are a reasonable compromise for commute convenience and should be allowed.)
However, I've assumed part of the reason our school chose this option is that most students live within a couple of miles.
I'm curious where you found the following: "New guidance from DfE even recommends schools with large commuter populations to consider workarounds like handing in brick phones/keeping them switched off in their bag throughout the day." The only guidance I can find states that schools must ensure that students cannot access their phones during the school day, and they would at least need to be in the locked pouches in their bag to achieve that.
I don't blame my school for adopting this policy. I blame the government and think it's up to parents to contact their MP to try to change the government policy to allow brick phones turned off in bags. I can understand the school not wanting to spend money on pouches or lockers, or time on handing phones in and out at the beginning and end of the school day, but instead spend the money and time on learning, especially if they anticipate another government might roll it back in the nearish future. (I'm not even pro or against the current government, I just think this particular policy was rushed through without consideration of its practical consequences for schools, students or parents.)
My best advice is to look for phone boxes along the route, as I have found that now that I look for them, there still are a few around, not on our particular route, but maybe you'll be luckier than us.
Also, I think our school probably also is dealing with it by slightly turning a blind eye to the fact that students might have them switched off in their bags. They aren't actively searching bags or anything, it's just that if phones are seen or heard, they are confiscated and the student gets detention. And so I think many students are just brining phones anyway. Unfortunately, my kid is also one of those who adamantly refuses to do so on the grounds that he feels he should follow the rules, and I can't really argue with that.
I do wonder if sometime something preventable will happen to a child due to the policy and then it will make the news and get reversed.