How many exchange accounts may I have on my iPhone. I work for two companies wanted to have both email accounts accessible on phone

Perhaps, unless the profile for one company excludes another profile from being installed. That sort of profile setup would prevent you from installing the second account.

If you use the MS Outlook app, you could sign in and out of each as needed, but that app will not allow two simultaneous logins. You can try and set up both up in the iOS mail app - if the first installs a company profile that precludes installing a second account with a profile, you will know when you try to setup the second account.

As with gmail, yahoo, or any other email service, there is no limit to accounts in the iOS mail app. The only thing that would prevent multiple exchange accounts is the exchange security profile that an account installs when setting up the exchange account. If the exchange account(s) do not use a company security profile, then there should be no problem with 2 or more exchange accounts.