Since there are 3 words in that name, I wouldn't necessarily call it a "premium" domain. Usually a premium domain, in my definition, is a one-word domain or possibly 2 words, depending on the words though.
For this domain, for "online seo audit" there are 140 searches per month according to SEMrush. About $7 per click for the CPC pricing. If you wanted to buy the traffic and clicks, that would put it about $1,000 per month. There other variations of the keyword, though, such as "seo audit online", again with 140-150 searches per month.
The issue with "seo audit online" is not necessarily the number of searches, though. The issue I see is the potential use for the domain (and that's a BIG factor when it comes to value of a domain). You see, someone searching for "online seo audit" is going to be wanting for a FREE audit. There's no real way to make money from providing a free service. However, I know you can get the SEO leads and sell them for a profit. But, those leads are people wanting a free online SEO audit, so they're not probably going to be your typical $5,000/mo SEO client. It might be tough to get them to even pay for an SEO audit. They're looking for an 'online seo audit'.
So, as you can see, it's not just about how many searches per month and daily organic searches. The value is in the potential use of the domain, and how you could make money by putting an "online seo audit" on that domain. The same goes for any domain that could be used to sell a service or a product. If it's going to make money, a lot of money, then the domain can be more valuable.
So, given the potential use for this domain, the user intent of the keyword, and that it's a 3-word domain, I would put the value at about $2,000 on the retail market, $500 for wholesale price.
I really wish this was seoaudit.com, and not onlineseoaudit.com, as seoaudit.com would be more of a 'premium' domain if you were able to find the right buyer.