i'm seeing difficulty of 30-40 for cheap phones (depending on country): https://moz.com/explorer/overview?q=cheap+phones (watch the video that pop's up from Moz's chat helper)
Check out https://moz.com/help/guides/keyword-explorer for more in depth info on how the scores are calculated.
How is the Difficulty score calculated?
Keyword Difficulty takes into account the Page Authority (PA) and Domain Authority (DA) scores of the results ranking on the first page of Google for the given query, as well as modifying intelligently for projected click-through-rate of a given page (putting more weight on higher-ranking, more visible pages and less on lower-ranking, less visible pages). The formula also accounts for newer pages on powerful domains that may have DA scores but have not yet been assigned PA values.
What is Opportunity score?
Opportunity Score is designed to calculate the relative Click-through-Rate (CTR) of the organic web results in any given Google Search Engine Result Page (SERP). Google SERPs that have very few non-traditional ranking features and are more similar to the classic “ten blue links” only model will have very high Opportunity Scores. SERPs that have many features - like images, ads, news results, answer boxes, knowledge graph panels, etc. - will have much lower Opportunity scores. We use an averaged CTR model derived from our anonymized clickstream data to build this useful metric and apply it based on the features we see in Google’s results.