function of probability for normal distribution

Dear Greg Snow,

I'm a biologist trying to write a mathematical formula for a doubly
truncated normal distribution to be used in the language "R". I realise this
is simple stuff for a mathematician but I'm stumped. 
Wikipedia gives what seems a fairly simple formula - with function = maths
with mean and standard deviation - but also phi - WHAT IS PHI !!?? -
especially how do I write this in "R" and why is the top "phi" in italics ??

Hoping you can help.

Yours sincerely,

Jeremy Clark

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