The second-best charge range for batteries inside smartphones is 45% to 75% — probably a lot more realistic for most people on a day-to-day basis than 65% to 75%.
You could even develop a daily routine to plug in your phone at particular times to keep its charge within those levels. Just plug it in whenever you can, even if it's for a few minutes, and you'll be fine.
"Partial charges cause no harm," according to Battery University.
But you have some wiggle room. If you typically keep your phone's charge level between 25% and 75%, you most likely won't cause too much long-term damage.