It's kind of like you're saying say say. This is what you say when you answer or greet someone on the telephone. There's a strange story about this. One reason you say 申し申し is because it's hard for foxes to say. So, you're confirming that the other person isn't a fox. The other explanation is that operators would say this, letting the person know on the other line that they're talking by saying "say say" but in a humble way. Either way, this is a telephone hello, so say it next time you talk to someone on the phone who is Japanese... just to make sure they aren't a fox.

We usually don't use kanji for this, so don't use it when you're writing. But you'll probably run into it in the wild so it's good to know!

This word uses the reading you learned with the kanji. You should know it already.