phrase//2 and phrase//3

Under construction. See Scryer's implementation. Either

add to TS 13211-3 7.14 Grammar control constructs as 7.14.13 or
add to the Prolog prologue as a non-terminal.

Both options are justified by 5.5.13.

7.14.13 phrase//2, phrase//3
The grammar body element phrase(NonTerminal__1, Arg1) describes phrase(NonTerminal) where NonTerminal is constructed by appending the additional argument Arg1 to the arguments (if any) of NonTerminal__1.
The grammar body element phrase(NonTerminal__2, Arg1, Arg2) describes phrase(NonTerminal) where NonTerminal is constructed by appending the additional arguments Arg1 and Arg2 to the arguments (if any) of NonTerminal__2.

EXAMPLE —