Hi,
There is some information about this around the Internet. It’s certainly possible, and not necessarily expensive.
I have this set up here, which works well:
• Technics SL1800 turntable - plugged into a:
• Behringer UFO202 audio adapter. This has a Phono amp built in, and can also switch to line-in - plugged into:
• USB-Lightning hub (you can use just a plain USB-Lightning adapter, but I preferred to have power available, so a hub with two Lightning ports is useful) - connected to:
• An iPhone, I use an old redundant iPhone 6S so I can leave it all plugged in, and free up my normal iPhone - running software:
• AirChord app, which will connect the audio input to your airplay speakers:
• a Stereo pair of HomePod Minis.
Also have a search on Reddit, there’s quite a following for the AirChord app there.
As you already have a Phono amp, you can just use that and switch the UFO202 into line-in mode (it’d probably sound better). There is the UCA202 which is line-in only, but is weirdly slightly more expensive (they’re both only around £20 here in the UK though).
Hope that helps.