User created invoices for a project phase, but does not want any taxes to apply to them.
Your invoices show the taxes because you have added them at the project level in Projects > General > Billing Options. Set the Main Service Tax and Main Expense Tax to zero so that the invoices you create do not add taxes. You can set them directly for the phase or at the parent project level, and then choose to apply it to the child projects. Check the Core Help for details. The change applies to new invoices you create, so you may need to recreate the existing ones.
Note: If you also have taxes at the item level (Tax 1/2/3 for time or expenses), you may need to remove them too from the time and expense entries. Then you can recreate the invoices.