Jexi follows a man (Phil) who has social anxiety. He's got a decent job, but doesn't have a girlfriend or many friends in general. All that changes when he gets a new phone.
His phone comes with a digital assistant, similar to Siri. Except this assistant has a bit of sass to it. At times, the assistant will insult him, or do things for him without asking. All in all, it's definitely a YouTube-level gag. It's funny at times. But the movie seems determined to make a point. As he builds a relationship with those in his life (which his phone encourages him to do, initially), Jexi starts to get jealous. She begins manipulating Phil, trying to "salvage their relationship". She intentionally sabatages his job and romantic relationship, which breaks him down until he eventually decides to man up and solve his problems in person (without a phone).
If my summary sounds terrible, that's because the movie is. I don't even have many complaints outside of "it was made". Easily one of the least enjoyable movies of the year.