Could you please share a bit more about the issue on your side?
Do you want to change the date icon size within the Date picker control?
If you want to change the date icon size within the Date picker control, I afraid that there is no way to achieve your needs in PowerApps currently.
If you would like this feature to be added in PowerApps, please submit an idea to PowerApps Ideas Forum:
Which version is PowerApps Mobile app within your Mobile device?
I have made a test on my side, and don't have the issue that you mentioned. The screenshot as below:
The version of my mobile device is Android 8.0.0, the version of PowerApps Mobile App is 3.18091.14.
Please check if the version of PowerApps Mobile App within your mobile device is the latest version, if not, please upgrade it into the latest version, then check if the issue is solved.
Please also take a try to turn off/disable the "Improved app rendering (final validation)" option within the Advanced settings of App settings, then check if the issue still exists.
You could also take a try to uninstall the PowerApps Mobile App from your mobile device, then re-install it again to check if the issue is solved.
We have the same issue when publishing the app. In preview when editing it looks like it should, but when access when published it cuts off. We have three date pickers in this app and it's the same issue on all three.
please review this thread and let me know if the accepted solution works for you.