For my on phone mapping I use Roadtour Outdoors GB (only iOS). For £14.99 a year you get 1:25k and 1:50k OS which you can either use on the fly or download and use offline. There is the ability to use it on a web browser too with a very (very) basic route plotter. If they developed the web browsing aspect, it would be pretty good. On the iPhone/iPad app you can overlay Google satellite and maps as well as open street map and open cycle map. TBH I kept it from some years back when I used an offer on the National Park maps and couldn’t be bothered to change it. I don’t plot routes on it as I still use the late lamented Tracklogs for plotting and printing. I use in the field for position and detail for route finding.
https://outdoorsgps.com/
https://outdoorsgps.com/