Recently, the NLM Technical Bulletin published a Skill Kit about phrase searching in PubMed.
The skill kit includes these tips:
• Search the phrase first without quotes or search tags.
• Check Search details to see how the search was translated.
• Use quotes only when your phrase is broken apart.
• Sometimes even quotes won’t work because not all phrases are recognized as phrases.
For examples and more information, read the full skill kit article.