Only 1 Comp in Phrase but 21m Broad...

Yes, only 1 other website competing within phrase tags but unfortuntely 21m broad!

Should I go for it? Whitehat or will I have to go blackhat?

PS - Allintitle = 5,800

Allintitle = 5,800 (phrase) is possible to beat white head, the upper limit would be about max 10,000 (not recommend). But you need to analyze exactly the top 10 ones for your phrase. If there are several Authority sites there, you can't beat them. Also, check if you can get a related domain name or not. You need also to check how many linked back to each of the top 10s.

Top 2 are ezine articles and #3 is a yahoo answers page... what do you reckon?

Also while we're here, how about this other term I found:

BROAD: 576,000
PHRASE: 48k
allintitle: 167k

Top 10 are a mixture of 1,2,5,3 PRs

Ezine articles are a great entry point for you for the top 10. Write your own quality articles and beat the existing ones.

As per your second question, I would need to see the full picture of the top 10. But a phrase of 48k is beatable. The PRs also sound good although you have a hard to beat PR5

Said that, Google seems slowly moving to ignore PR's. Go to 'seoroundtable.com' and look out for the related video.