Since these trees were planted four years ago and some appear to be dead, I'd be more inclined to think they were either improperly planted or that there is a site issue. There also seems to be a lot of competition from shrubs that were planted very closely. Woody plants often have a long delay before they show symptoms of root damage or incorrect planting, this can take years in some cases. You didn't mention how you previously confirmed phytophthora issues but if it wasn't confirmed by a certified arborist or the Pest ID lab, I would be hesitant to make that diagnosis. 

The Pest ID lab can be contacted directly via <personal data hidden>

Having an arborist come out might be appropriate, so that they can see how the trees were planted and if there are any site issues. Arborists can be found at treesaregood.org

Thank you, I’ll let the gentleman know.  

 

When he came into the office asking about the trees, he mentioned that years ago he dropped off plant samples to the MSU diagnostic lab and the report came back as phytophora.

That's good to know. They may be able to dig up the previous report and give some information on what not to plant if that was the issue. I still wouldn't rule out issues with soil compaction, drainage, or improper planting. They will likely ask him to send samples again.