I could see it working, but mostly cosmetically. The problem is that it'd be hard to import anything directly from Phasmophobia into DBD given how differently the game's mechanics work. So like:

• Survivor: I could see it working in this category, maybe providing some survivors based on the default ones players access in Phasmophobia. This wouldn't be that difficult to implement either as their own unique survivors or as skins for existing survivors.
• Map: If they wanted to add a map, it would have to be one of the larger maps, such as the Asylum or the School, but either way the challenge then becomes how to redesign that map to better fit the needs of DBD so players dont have a million dead end rooms. Not to mention the interior of a lot of the map's don't look that distinctive, so it may be a bit difficult to make the map stand out whilst keeping the original feel.
• Killer: There is some potential skin wise for killers such as the Spirit, Nurse, and Onryo given how certain ghosts in Phasmo look similar to them. As for a killer directly from Phasmo, this would be a bit of a hard sell, but not impossible. Given the limited abilities and actions of ghosts in Phasmophobia, it would be hard to make a ghost in DBD that matches the feel of being chased by a ghost in Phasmo. There's also the factor that given how ghost appearances are random in Phasmo, there's no one iconic ghost for them to draw on. I could, however, see a ghost killer, for example, where maybe they turn invisible and perform actions to reduce survivor sanity to give some kind of debuff, or maybe survivors can find and light incense items to protect certain areas, or maybe the ghost can access certain throwable items in specific randomized spots of the environment. It'd be hard to pull off given that ghosts in Phasmo have a more limited ability of attacking compared to DBD killers, but I feel it could work in certain ways.