LTE+ means you're phone is using more then 1 4G band once the available bandwidth exceeds 25 mhz the + logo will appear it's commonly known as carrier aggregation to see what bands your phone is using you can dial *#0011# as you can see in the image my phone is using band 3 and duel band 7 totalling 55 mhz as it's over the requirement of 25 mhz my phone displays 4G+ hope this helps and isn't too complicated 😂
