If it were registered it would have a ® next to it. So no, it probably isn't registered but that does not mean Phillips Data, Inc. does not hold a legal trademark ™ on it.
Again they legally hold a trademark ™ on it as long as they can prove that they held their trademark prior to use by public/others. Public is in reference to common words/terms/phrases which "blesta" is not, it is obviously unique, so that leads to others which includes individuals and businesses using/referencing the term/word. Otherwise any use, reference, etc. requires their express consent or they can pursue legal action.
I think your original post was in reference to a post on WHT about a domain sale/appraisal. The simple answer is that anyone can own/hold the registration of a domain name even if it contains a trademark registered or not. Legal precedent says that they hold/own the registration of the domain not the name itself. Using the domain for business (active site) would require the consent of Phillips Data, Inc. or the content of the site would have to be unrelated to the original trademark and the owner/operator of the domain and site could also be legally required to place a notice of non-affiliation.
Really just ask Phillips Data, Inc. if you can use their trademark. Open a support ticket, email, or even call them. In most cases businesses wont mind as long as the use is not by a competing product/service or defamatory.