Whew and woo are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It’s suggesting what word you may want to save time, but quite often, its suggestions are pretty off base. They don’t help you out, but they do make you laugh.
Whew is an interjection. It is word used to express surprise, dismay, or alarm in response to someone else or other events.
Woo is a verb. It means to attempt to attract someone you’re interested in for a romantic relationship or affair. The stereotypical ways of wooing include gifts, attention, and/or flattery.
The following story uses both words correctly:
Winola was tipped off that Nestor, her roommates’ cousin, wanted to ask her out. Upon reflection, his attention and attempts to woo her were clear.
The next time everyone was at the pub she took him aside and said she was interested in someone else. Actually, there was no one else, but she was trying to gentle. Nestor said “Thanks, but I don’t know who told you that. I’m seeing Felicity. We met last week.”
“Whew!” she chuckled, “I’m glad that’s behind us.” In her mind she was reeling. Why would her roommate set her up to be embarrassed like this?!
“Catch you later!” She acted like she knew someone across the room and walked away.