It's actually a complex question. The Libyan government and army is somewhat split and that's a nice way to put it. Some would say a renegade General is leading a bit of a rebellion there or at least, is one side of the Civil War.
That General is Haftar. There have been a number of articles on him here so the short answer, is Trump and Haftar had a phone call and some don't appreciate that. Some say we should only be talking to the UN recognized government, the GNA, Government of National Accord. It's complex. Haftar by the way, is a US citizen though, he wasn't born here. He lived in Langley VA. for 20 years, before that... he was in a jail, it is complex.
Libya’s Haftar says to fight until Tripoli militias defeated
https://english.alarabiya.net/en/News/north-africa/2019/05/26/Libya-s-Haftar-says-to-fight-until-Tripoli-militias-defeated.html
We are not officially on Haftar's side, Trump talked to him and said something like Haftar was doing good fighting terrorism.
https://www.france24.com/en/20190419-libya-trump-haftar-phone-call-tripoli (phone call article)
It's a story in itself that has raised some controversy.