Undergrad grades in PhD
Since you have not provided enough details in your question I will go with a generalised answer to this end. The answer to this question, however, is country- and organisation-specific. Further, it does also depends on the PhD advisor herself.
I am in academics for a few years now and I have seen some post-grads (not PhD) who do/did have bad grades during their corresponding undergraduate studies.
First, let's quantify what does a bad grade mean: On a scale of 1-10 (10 being the highest), bad grade would be, according to me somewhere within 4. &quot;Ok&quot; grades would be the ones falling in the range: 5-7, and above 7 is just great. As I said, this can be argued; but lets for the moment accept these as axioms.
So, if your grades in the &quot;bad&quot; category, then you should have something additional to show to the PhD selection committee or the advisor you are applying under. This term &quot;extra&quot; would mean something like a voluntary project that you did, maybe a collaborative work you participated in, or an article that you wrote with some others. Again, this extra stuff that you show may not be well-accepted but would definitely provide a soft edge towards the decision-making process. Also, note that PhD application might require a few recommendation letters if those letters could mention these extras to compensate for your bad grades, then you are okay I think.
If you have nothing to show as an extra component, then this might not be a good sign to have &quot;bad&quot; grades in the CV. A PhD position would expect someone to be serious in studies and highly motivated to pursue research.