Value of unpublished (i.e. submitted) papers?
The rule of thumb with writing a CV is to keep things relevant. If what you are writing is relevant for the purpose you are writing your CV (you should really have a template CV, and customize it for each application), then yes add them.

So a couple of ways how I could see that being relevant for you, specifically:


you mention applying to a PhD program, so it might be relevant to show whoever is taking the decision that you have worked on something similar before
in a similar way, it could be meaningful to show that you have some research experience, as opposed to other graduates that have 0 research experience.
if your manuscript in review has been uploaded to a preprint server (like arXiv or BioRxiv) then you might even be able to showcase the work you have done.