Obsession
Obsession is the overarching theme of Mr. Harrigan's Place and is responsible for the central conflict of the story. In the novella, Craig is obsessed with obtaining a new phone - specifically, an iPhone. When Craig finally gets an iPhone several years later, he becomes obsessed with getting his elderly neighbor Mr. Harrigan an iPhone. In turn, Mr. Harrigan (just like Craig) becomes obsessed with his cell phone and is ultimately buried with it, which causes his soul to transfer to the phone and reach out to Craig when he calls. Craig's obsession eventually causes the deaths of two people and other negative consequences.
Karma
Another central theme in the novella is karma. In the novella, a drunk driver is coaxed by Mr. Harrigan's cell phone to commit suicide. People obviously make mistakes, but drinking and driving are illegal and can injure or kill countless people (just as the drunk driver killed a teacher in the novella). Similarly, a bully is also coaxed into committing suicide by Mr. Harrigan's phone. Bullying people isn't illegal, but it is morally wrong and has quite a few unintended consequences - most importantly the irreparable harm that could result from it. Their deaths - as tragic and unfortunate as they are - are karma for their deplorable and damaging actions.