In a phrase search, the search terms are normally supposed to appear successively in a certain order, i.e. a search engine looks in the references for a given exact succession of symbols. In some databases, the concept of a phrase can be interpreted less strictly, so the words do not need to appear in a definite order, only successsively. The manner of presentation for a phrase search depends on the particular database. It is also worth checking in instructions of the database how to take into accout different expression of a word i.e. plural forms, other conjugations, spellings etc. in phrases.
Many search engines ignore prepositions, conjunctions and other common so-called 'stop words' written in a search, as they normally do not have an effect on the relevance of the search result. Instructions given by the databases have a list of these of words and advice about what to do if, for some reason, a stop word must be included in the search, for example, if it forms an essential part of the phrase.
Often the phrases are written using quotation marks, like in this example from Web of Science. Without quotation marks the search words are combined with the AND operator in this database. Source: Thomson Reuters - Web of Knowledge (Web of Science) <http://apps.webofknowledge.com> 10.2.2017.