Just a remark to always benchmark your code to make this statement. As newer releases of .Net Core also Regex gets faster and faster.
So better stay maintainable and readable and let the performance guys do their work
References:

• https://devblogs.microsoft.com/dotnet/regex-performance-improvements-in-net-5/
• https://devblogs.microsoft.com/dotnet/regular-expression-improvements-in-dotnet-7/
• https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-8/#searchvalues which is/will be used by Regex under the hood

discard "Skip(0)", it's a nop

Resizing input references is bad practice.
This will be not obvious to the caller and will lead to strange bugs. Hopefully it is documented somewhere.
Better create new array.

"phrase" is never changed so it is enough to just iterate over "phrase" instead of allocating extra memory for chars.