Modern batteries don't need to be conditioned, and don't require special care.
Actually they do. After the conditioning at the manufacturer the way you finish conditioning them is below.
Just charge them up whenever convenient.
And I'm not just trying to be funny. Just use them and charge when you need to. That conditions them. Li batteries continually change throughout their life for a plethora of reasons. Keeping them from the extremes means you get more total energy delivered.
Some basic thinks to keep in mind:
1. Don't charge if the phone battery is much below 0 degrees Celsius. Lithium plating occurs which reduces the available Li for charge shuttling which lower capacity.
2. Besides avoiding high temperatures in general, avoid charging at high temperatures. Someone asked about 40 deg C. If you must charge at that temperature, charge for as short of a time as possible. This means use the 1.3A charger that came with the phone rather than the wireless charger or another slower charger. It is the length of time charging at high temperature that does the most damage. This is one reason why Nissan didn't expect to have the issues with the LEAFs in hot climates. Their tests didn't slow charge the battery like many of the owners did.
3. Don't discharge your phone until it shuts off very often. Even once/month is excessive. If it seems like your phone doesn't have as much battery life as it used to then try it but don't over do it. The only purpose of discharging until the phone shuts off is to calibrate the battery monitoring circuitry. Since most of the phone batteries have a relatively steep drop in voltage from full to empty the circuitry can estimate state of charge reasonably well with voltage. (This isn't the case with LiFePO4 type cells which are not used in phones and laptops.)
4. Charging to 100% and holding there does shorten the life of the battery but it isn't really a huge amount. Most people wouldn't even be able to tell the difference. I have phones over 4 years old and they still have a respectable battery life. I charge mine every night. If I could program it to only charge to 95% I would but that option hasn't been given us so I don't worry about it. I also never worry about getting a phone with a replaceable battery. They last so long that it doesn't matter any more.
On a side note: partially charging/discharging NiCd batteries doesn't damage them. What it does do is fool the charge circuitry into thinking that they have reduced capacity because the voltage takes a sudden drop around the point that they usually get recharged at. If the circuitry had the smarts it would allow a deep discharge which would recover all of the capacity. A similar thing happens with NiMH batteries. I have done this many times over the years and gained all the capacity back in line with what they would have if they had been discharged completely each time.