After you purchase and install a data/calls/texts eSIM, you can check your phone number directly from your device settings.
On iPhone
Open Settings.
Tap Cellular (or Mobile Data).
Select the eSIM you have installed (under SIMs).
Look for My Number or Phone Number.
On Android (may vary by manufacturer)
Open Settings.
Go to Network & Internet or Connections.
Tap SIMs, SIM Manager, or Mobile Network.
Select your eSIM.
Look for Phone Number or My Number.
Alternatively:
Go to Settings > About Phone > SIM Status.