I'm using and old Android 4.1.2. However as I indicated, neither my 2010 Accord, 2014 Accord, nor my 2011 Ridgeline dropped calls using the same phone. My 2018 Accord drops calls frequently, almost every time I use it.
I still have my 2011 Ridgeline and have no issues with dropped calls. So, based on past experiences I don't think it's a problem with the cell towers or phone hardware/software. However, it is possible that the 2018 Accord software or hardware may not work well with my version of Android. BTW, every other Bluetooth feature works fine (contacts, favorites, call logs, text, etc.), and the quality of the calls is good.
What's strange is I don't recall anyone else mentioning the problem, even on the other Accord message boards. It's very irritating but, I'm not willing to buy a new phone because I'd be highly upset about wasting money if the 2018 Accord is the problem.