First, start with the terms x and 7, the expression calls for their sum so addition is the needed operation. Then, 4 times the sum means that 4 must be multiplied after x and 7 are added. So because of PEMDAS parentheses are needed around x+7. Therefore the expression is 4(x+7).
If it's a sample of something, it should remain as true to the original product as possible. There should be no difference in quality between the sample cell phone and the regular cell phone. If there was, that would defeat the purpose of it being a sample.