How does a low quantitative score on GRE general exam affect admissions to mathematics PhD programs?
Unsurprisingly, mathematics PhD applicants are rumored to have very high GRE general test quantitative scores.

I found a few links by web search where PhD programs list the average GRE scores for their students. (Everyone, please feel free to edit this to add more.)


Penn State: https://www.math.psu.edu/grad/phd/faq.php
Duke: http://gradschool.duke.edu/about/statistics/mathematics-phd-admissions-and-enrollment-statistics
U Penn: http://www.math.upenn.edu/grad/graddata.html
U Maryland Applied Math and Statistics: http://www.amsc.umd.edu/join_us/faq.html#Tests3
Georgia Tech: http://www.math.gatech.edu/academics/graduate/faqs-graduate-admissions#MINGRE


These sites all show average quantitative GRE score is in the high 160s, which corresponds to about the 90th percentile (which was around 795 out of 800 on the old scale). So, if these statistics are accurate, the rumors are true. 



Now, for the more personal side of the question. You asked if the scores are "enough". Most schools have no firm minimum score. If you have sufficiently good credentials, you can overcome the low GRE score. What you will need, certainly, are very good letters of recommendation. 

I would include a statement about anxiety in your personal statement, because even if the committee has heard it before, they haven't heard it from you.

You may also want to make sure you have diversified your applications: don't just apply to top-25 departments. There are a lot of perfectly fine schools lower in the rankings, which may not be as broadly strong but which may be strong in particular areas of interest to you.