How to replace dash in a column of numbers with a space and add a prefix

Example:

A1: 51-4001
It should show in B1: PHM51 4001

Thanks!

Try
="PH"&SUBSTITUTE(A1,"-"," ")

Thank you. It sort of worked. Here's what displays in B1:PHMVendor Part Number
But when I drag the cell down to B2 it shows the right info but in the wrong cell:PHM51 4001
How can I make it work to display the right info instead of the PHMVendor Part Number verbage?

Make sure calculation is set to Automatic.

Not sure how to set it to Automatic. Please advise.

On the Formulas Tab, near the Far Right side is "Calculation Options"
Click that and choose "Automatic"

I just checked and it was already set on automatic. I was hoping I could send a screen shot but it won't allow me to. Maybe there's another setting that's off?

Thanks. I did notice that also before I entered the formula and made the change to add the M and those were my results.
For some reason it gives me the PHMVendor Part Number in that cell instead of the correct data that displays when I drag the cell down.

I just realized why it didn't work. I was in a spreadsheet created by another user with some restrictions in it. When I copied the data over to a blank spreadsheet it worked. But now I need to know how to copy this formula to the cells below it. The numbers are random numbers - not in a particular order.
For example:
54-3500
53-3402
Thanks.

Perhaps A1 is a header, and you really want to refer to A2

="PHM"&SUBSTITUTE(A2,"-"," ")

Thanks all. I just figured it out. When I inserted a header row above the cells with data dropped the formula as a header in B1 - then dragged the cells down - it displays the correct data for each cell. Thanks for your help!

You're welcome.