Same thing happened to me and it's so freakin' frustrating. Lost all my playlists while I was on vacation. I'm home now, at my computer, and here's how I fixed it.
Connect your phone to your computer (I'm on an iMac), open iTunes, click on the device (I have an iPhone 6+). Under "Settings" on the left (not On My Device) click "Music" and select "Sync Music"--> "Selected playlists, artists, albums, and genres". This looks more like the screen I've used in iTunes for years. I was able to put the playlists back on my phone.
I've been a huge Apple fan and have had an Apple computer since the mid 80's. I have an Apple tattoo on my hand! But the quality of their products has really declined in the years since Steve Jobs' death. They need to work smarter and put out innovative products without glitches and that are intuitive, or they are going to fall behind and become another giant that fell. I really don't want to see that happen. Apple!!! Fix these problems!!!!