Charge whenever you can, or need to. It really doesn't matter at all to care about the cycling thing unless you store the device somewhere and do not use it at all, in that case, once in 30days, you need to fully drain the battery by using it of courses, and then fully recharge it straight up which is equal to 1 cycle.
Keep in mind that batteries nowadays are design to go about 500 cycles, that is, if you burn 1 cycle a day, you will have your battery in a good shape for a little less than 2 years or to be exact, 1 year and 135 days which will make up the 500 cycle. After that, your battery will only hold 80% of true charge.
So but, the more cycle you burn, the more shorter your battery life span is getting, and if you don't kill one cycle at least a day, your battery will end up losing keeping charge capabilities anyway after 2 years as it's a Lithium-ion battery which gets affected by weather temps and the device temp as time goes by.
So the balance is, just use your iPhone normally with an average of one cycle a day.

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