The easy way is to use iCloud
Set up iCloud Drive on all your devices - Apple SupportOfficial Apple Support › icloud
Then setup "Optimize iPhone Storage" for all your photos / videos
Manage your photo and video storage - Apple Support
If you do this your iPhone will copy the original photos in the iCloud and smaller copies to your iPhone.
The nice thing is that you don't have to do any thing and the size will automatically be adjusted if you get more new photos.
The manual way could be to export all your photos from your MacBook in a smaller version (smaller resolution / quality) and import them to your iPhone.
A problem is that an export will create a new file and this file will get date & time from the export, therefore you have to change the date & time for all these files.
There are tools that can do this for you.
But you must estimate how many photos you may get in the future and pick a file size that would still work with your future photos. If your estimate is wrong you do the file size reduction again.
I have close to 35,000 photos on my iPhone, that has only 32GB memory.
I would not do this manually, but must decide if you want to pay for extra iCloud storage or if you want to take time and risk to do it manually.
iCloud+ plans and pricing - Apple Support
Ralf