Hi, I am an airline pilot payed with W-2. Many times I have to use taxis and Uber/ Lyft to move from hotels to airport. Can I declare these expenses?

For a 2017 tax return you could use that expense as a job-related expense--subject to the 2% of AGI floor--for 2018 and beyond the job-related expense deduction has been eliminated.

For 2017:
JOB RELATED EXPENSES
Only the amount of job-related expenses that are OVER 2% of your adjusted gross income get added to your list of itemized deductions, which still must exceed your standard deduction in order to make a difference on your return.  This is kind of a hard deduction to get.  If you need to enter these, go to Federal>Deductions and Credits>Employment Expenses>Job-Related Expenses.

Any reimbursement for those expenses?

For a married person to have enough itemized expenses to exceed the $24K standard deduction, and have your job related expenses exceed 2% of your AGI is gonna be tough. Besides, starting in 2018 job related expenses for a W-2 job have been eliminated. It's estimated that less than 10% of tax filers will see any benefit from itemizing starting with the 2018 taxes.

As an aside, don't most airport hotels have complimentary van service to the terminals?

wouldn't that be a commuting expense?

If the pilot is away from his or her tax home, the travel expense to and from the airport to the hotel is deductible travel.  If the pilot is at their tax home, they are non-deductible commuting expenses.  See for example this tax court case involving a United Express pilot. https://www.watsoncpagroup.com/images/pdf_up/TCSummary2010-127Commuting.pdf

The pilot maintained a home and farm in Tennessee but regularly was assigned and flew out of Dulles, and maintained a residence in Sterling VA to be close to Dulles.  Since the pilot was regularly assigned to fly out of Dulles, that was his "tax home" and travel from Tennessee to Sterling and from Sterling to Dulles were non-deductible commuting.  Neither transportation, lodging costs, or meals are deductible.  However, if the pilot stays overnight in a remote city (the other end of his route) that is "travel", and the pilot is allowed to deduct meal and lodging expenses as well as transportation to and from the airport.

Of course, this only applies to 2017 and earlier, the deduction for unreimbursed business expenses was eliminated for 2018 and forward.  You or your union should be discussing new arrangements with your employer.