He said to his wife: If you check my mobile phone you are divorced

If a man says to his
wife: If you check my mobile phone you are divorced, the basic principle
is that a revocable divorce (talaaq) takes place if she checks it, and it
is not possible to cancel that. He has to warn his wife against checking
the mobile phone lest divorce occur. If she does check it, one revocable
divorce occurs and he may take her back during the ‘iddah. 

See the answer to question
no. 105438. 

Some scholars are of the
view – with regard to this basic issue – that if the husband’s intention is
to prevent his wife doing something, and he does not intend to divorce, then
it comes under the ruling on oaths (yameen), so he has to offer expiation
for breaking an oath (kafaarat yameen) if she does that, and it does not
count as a divorce. This is the view favoured by Shaykh al-Islam Ibn
Taymiyah (may Allah have mercy on him) and a number of scholars, and it is
the more correct view. See the answer to question no.
82400. 

Each person knows his own
intention best, and Allah is watching over him, so it will not avail him
anything to deceive himself and claim that he did not intend to divorce at
the time he said it, if that was indeed his intention. 

And Allah knows best.