How do PhD admissions look at A- grades from a Master's student in Math? I'm currently graduating with a M.S degree in Mathematics and looking into applying to PhD programs in Mathematics this Fall. 

My GPA overall is in the 3.90+ range. Course grades are either A- or A. About 30% of them are A- with two or three courses I would assume to be critical. 

I was wondering how PhD admissions view these A- in general. Talking with some of my professors and adviser, either admission committees would take A- as an A (not care) or have some concern, especially in those critical courses. Within the department, A- is more of "you did what you're supposed to, but you could've done better". 

Overall, I think I have a strong application (great recommendations, high Subject Math GRE score, some experience in research), so I'm not too concerned, but how concerned should I be?    

I will admit I'm being nit-picky, pedantic, and need to worry about more important things in life.
Your letters of recommendation will be much, much more important than the difference between an A- and an A. Spend your time on getting the strongest letters you can (and learning how to do this, if necessary).

Source: I have served on grad admissions for a top math department.