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I studied and taught different types of survey design. All survey methods have their bias. Telephone studies are typically generated to try and over come those biases. I know some of what is done having supervised a telephone based lab and dealt with massive samples and calling rules and the like to deal with the bias issues.
I would not be in the least bit worried with them having conducted a phone survey.
The questions they asked and the sample size would be a great deal more important then the fact that it was a phone survey.
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