If it is possible to say 'He earns twice as much money as she (does)' can we use 'less' to make a sentence with an opposite meaning 'He earns twice as less money as she'? Are these sentences correct: I have twice as many cell phones as he has. I have twice as few cell phones as he? Thank you in advance!
There are two issues here. (1) 'Times' expressions of the kind 'twice as ... as', 'three times as ... as', 'a hundred times as ... as', etc. are not used with the comparative form of the adjective, but with the simple form. In other words, we do not say 'twice as more as', we say 'twice as much as'. Thus, 'twice as less as' is incorrect in the first place because it is ungrammatical. (2) It is incongruous (though not ungrammatical) to say 'twice as few as'. This is better put positively by saying 'half as many as'. This is preferable because it is clearer and more natural to use a positive expression of quantity ('many' rather than 'few').
It is not possible to say that and be understood; the sentence is meaningless. If you mean that he has, say, four such phones and you have two, then you need to say either: He has twice as many cell phones as I have. or: I have half as many cell phones as he has.
I'm sorry, but this sounds very strange to me. Perhaps that is because I speak American English. Or maybe it isn't. See the discussion in this thread: It operates at four times less pressure than the old ones.
I have not heard the expression "twice as less/few". I would say "half as much/many". I am familiar with the expression "three times less than ..." or "ten times less than ..", meaning 1/3 or 1/10, but I do not use it myself because of the potential for confusion. It's not common, but I hear it now and then, and it seems to have a long history. Google Books contains a number of examples, including this one from a book published in 1742: .03 is ten times less than .3 A complete and compendious treatise of arithmetick, vulgar and decimal. By Thomas Clarke (accountant.)