While you're not wrong the benefit isn't worth worrying about. That advice used to be very true, but it's really no longer applicable (for any phone newer than 3-4 years old).

Storing a lithium battery at 0% or 100% makes no difference any more - and while charging 30 to 70% might get you a marginal increase in life, it's not worth the hassle.

The reason is modern lithium batteries never let you fully charge them or fully deplete, what you see as 0 to 100% on your phone is actually more like 10 to 90%.

What really kills your battery these days is heat.

Sadly that's hard to control, but the rule of thumb is the longer it takes to charge your phone the healthier it is for the battery. Faster charging = more heat. Quick charge 3 (sometimes called turbo/fast charge) can reduce lifespan further.
So for a big charge (almost drained to 100%) use an older low current charger and leave it overnight.

That said, phones are so disposable these days that even phones without a replaceable battery you'd have to try very hard to significantly reduce the batteries capacity before you got rid of the phone.

Most good phone batteries (so any mid-range or better phone) are good for 1500-2000 charge cycles. So even if you fully charged it 2-3 times a day 0 to 100% (well 10 to 90) that's still almost 2 years before you're going to get a noticeable reduction in battery capacity (around 80% of the brand new capacity), and another 2-3 years before your battery can only hold half of what it once did.