I mistakenly opened an IRA in 2019 and immediately closed the account ( within 48 hours) when I realized I was in error. I just received a 1099-R that shows the distribution and indicates it was funded in 2018. (wrong) by using the letter P in distribution code. How should this be noted on my tax return
A 2019 1099-R with a code "P" indicated that the contribution was a 2018 contribution and not a 2019 contribution. If the contribution was make in 2019 before April 15, 2019 then you might have specified that it was to be applied to the 2018 tax year.
If that is not correct then contact the issuer for a corrected 1090-R if it is in error. The IRS will expect to see the1099-R with a code P to be reported on an amended 2018 tax return and not on a 2019 tax return.
If the taxable amount in box 2a is $0 (or less than $0.50 such that it rounds down to $0), you can just ignore the form and just explain the circumstances to the IRS in the unlikely event that they question the contribution or distribution. With a taxable amount of $0, the only thing that should have been included with your 2018 tax return is that explanation.