If I charge my phone from 30% to 80% will it be my battery cycle? From what % should I start charging till what %?

Battery Health & Performance 

Your battery health is fine and is undergoing normal usage. Charge it whenever you want to. Try to not let your battery charge get below 20%. Your iPhone cannot be overcharged because it has a safety circuit built into it. You should change out the battery once your Battery Health reaches below 80% which will take over 2 years to reach under normal usage. Until then enjoy your iPhone.

Here is some more reading on an iPhone battery and its performance ➔ iPhone Battery and Performance - Apple Support

Axel F.