Q: Will I loose all of my progress by erasing my apple watch from my previous phone?

Hi

To retain and transfer historic Health and Activity data, your new iPhone must be restored from an encrypted backup of your old iPhone.

The process to follow is:

• Unpair your watch from your old iPhone using the Watch app (this also refreshes the watch backup, so it is fully up to date):
  • iPhone: Watch app > My Watch > General > Apple Watch > Unpair Apple Watch.
  • Unpair your Apple Watch and iPhone - Apple Support
• Back up your old iPhone via an encrypted method:
  • via iCloud (encrypted as standard) or;
  • via iTunes on a computer - IMPORTANT: choose to "Encrypt iPhone backup", so the backup includes sensitive data (including Health and Activity data, saved passwords, Wi-Fi settings).
  • https://www.apple.com/support/iphone/backup/
• Follow Apple's recommended steps to remove personal information from your old iPhone (you may prefer to only do this after you have verified that all data has been transferred successfully to your new iPhone and back onto your watch):
  • What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support
• Restore your new iPhone from the encrypted backup of your old one:
  • Restore your device from an iCloud or iTunes backup - Apple Support
• Pair and set up your watch with your new iPhone:
  • Choose to restore the watch from backup when offered the option during set up. This will restore most of your data and settings, with some exceptions (eg Apple Pay cards, passcode).
  • Set up your Apple Watch - Apple Support