Assuming that you have an Adobe cloud subscription, make sure that "Only Download Smart Previews" is enabled on the Cloud Storage & Sync tab of the Lightroom Settings.
Then make sure that your sync status is up-to-date, i.e. when you tap on the cloud icon it shows "Synced and Backed Up", then try the Clear Cache option on the Settings>Local Storage tab.
That should reduce the footprint on the phone to as small as it can reasonably be. But do you have any albums for which you've selected the "Store Locally" option? That obviously has an impact on how much space is used.