First, make sure that your HomePod is put in a location with solid Wi-Fi signal. Weak signals may cause the HomePod to have difficulty in maintaining a stable connection, so if possible try moving it near your Wi-Fi router or use a Wi-Fi extender to boost the strength of the signal.
Additionally, check if both your HomePod and iPhone are running on their latest software versions. Outdated software versions may lead to connectivity problems, so you should look for updates for your iPhone in the Settings app under "General" and "Software Update". For your HomePod, open up the Home app on your iPhone, tap on its icon and search for any software updates under "Software Update".
In case you keep facing trouble connecting devices together, resetting your HomePod to its factory settings is an option available. Unplug it, wait 10 seconds before plugging it back in and after a few seconds it should be reset. From there you must set it back up through the Home app on your iPhone again.
Lastly, contact Apple support if none of the above solutions help. They could assist with troubleshooting the issue further and will give you helpful information about whether repairs or additional help is needed.